The present invention relates to electronic equipment, and more particularly to electronic equipment installed outdoors.
Outdoor equipment enclosures for North America must successfully complete the standards of North America. Particularly, it is necessary to pass the following three tests relating to waterproofing, which are described in “Generic Requirements for Electronic Equipment Cabinets”, Telcordia Technologies, March 2000, GR-487-CORE issue 2, Section 3.28. Incidentally, Wind Driven Rain test is the most severe of the three tests.
1. Wind Driven Rain test
After water spraying on the front surface, right surface, and left surface of an enclosure for 30 minutes each with a rainfall intensity of 150 mm/hr and a wind speed of 31 m/sec, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm3) (1 gram of water) per 0.028 m^3 (m3) (1 ft^3 (ft3)).
2. Rain Intrusion Test
Water droplets accumulated in the surface grooves and the door frame shall not enter the enclosure immediately after heavy rain. After water spraying on the front surface and the two side surfaces for 15 minutes each, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm3) (1 gram of water) per 0.028 m^3 (m3) (1 ft^3 (ft3)).
3. Lawn Sprinklers Test
After simulation of sprinkler water spraying at a downward angle of 45 degrees on the front surface and the two side surfaces for 15 minutes or 45 minutes in total, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm3) (1 gram of water) per 0.028 m^3 (m3) (1 ft^3 (ft3)).
Meanwhile, IPX4 defined in international standard IEC/EN60529 (JIS C0920) also specifies as criteria that water splashing against the enclosure shall have no harmful effect. In other words, the provisions of “Generic Requirements for Electronic Equipment Cabinets”, Telcordia Technologies, March 2000, GR-487-CORE issue 2, Section 3.28 are unique in that they require the prevention of water penetration, in addition to the protection against harmful effect of water splash.
In addition to the waterproof standard described above, the outdoor equipment enclosure for North America should meet the requirement that an electronic component housed therein can easily be replaced. In other words, the enclosure should have a structure capable of replacing an internal unit including an electronic component within the enclosure, instead of replacing the whole equipment, for the maintenance and replacement of the equipment. This is also the specification that allows the installation of the enclosure first and then the installation of the internal unit afterwards.
Further, from the point of view of the cost and weight, the material of the enclosure is preferably resin. However, it is difficult for a resin seal enclosure to fully achieve radiation performance. Hence, it is necessary to ensure the radiation performance by providing an opening in the resin enclosure through which a radiation fin of a heat sink thermally connected to the electronic component, is partially exposed to the outside of the resin enclosure. Here, the heat fin may be splashed with water, but the water penetration into portions other than the radiation fin is not allowed.
In general, the electronic component and the heat sink are connected via a thermally conductive sheet. For this reason, it is difficult to remove only a board in which the electronic component is mounted for maintenance and replacement, so that the electronic component is removed and replaced together with the heat sink.
In JP-A No. Hei 10-173371, there is described an enclosure structure of electronic equipment that facilitates heat conduction from the inside to the outside of the enclosure. The enclosure structure is designed to improve the efficiency of radiation from the inside to the outside of the enclosure, by providing a heat sink for radiating heat from the inside out, in which a radiation surface of the heat sink is exposed out to the bottom of the enclosure. However, this structure uses a packing (O-ring) for waterproofing. The use of the packing requires precise control of the amount of crush of the packing, thereby requiring a lot of screws for tightening the packing. Further, it is also necessary to manage a tightening torque. Consequently, it is difficult to easily install and remove the internal unit.